Vibrational Excitations of Glass Observed by Helium Atom Scattering

W. Steuer (1) , A. Apfolter (1) , M. Koch (1) , W.E. Ernst (1) , E. Sondergard (2) , J.R. Manson (3) , B. Holst (1)

1 Institute of Experimental Physics [Graz]
2 SVI - Surface du Verre et Interfaces
3 Department of Physics and Astronomy [Clemson]

In this paper we demonstrate a new application of helium atom scattering: the investigation of amorphous solids. Recently, we observed an excess density of states in the vibrational spectrum of the vitreous silica surface using inelastic He-atom scattering. A surface phonon spectral density was readily extracted from the recorded data and the excess density of states was attributed to the surface manifestation of the boson peak phenomenon of disordered structures. Here we present further data analysis and show that the intensity of the surface boson peak at constant energy, i.e., ½zz(¢E = const.,¢K)/½Debye, strongly depends upon the parallel momentum transfer with a maximum in the neighborhood of ¼ 1 nm−1. In contrast, the position of the maximum intensity of the surface boson peak shows negligible ¢K dependence and is seen as a dispersionless mode at 3.7±0.4 meV. Measurements of the width of the surface boson peak are also presented.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

W. Steuer, A. Apfolter, M. Koch, W.E. Ernst, E. Sondergard, et al.. Vibrational Excitations of Glass Observed by Helium Atom Scattering. 12th International Conference on Vibrations at Surfaces, Jul 2007, Erice, Italy. pp.224003. ⟨hal-00504504⟩